IBM RT Series Hardware Reference Manual page 101

Color Plane Select Register
X'OlS4'
Write Only
Color planes can only be written or read by the system if the corresponding plane select bit is
active.
If
more than one plane is enabled during a read operation, only the lowest numbered is enabled to
the I/O channel.
Bits 0-3 Color plane select
Bit 0 1
=
Plane select 0
Bit 1 1
=
Plane select 1
Bit 2 1
=
Plane select 2
Bit 3 1
=
Plane select 3
Bit 4 1
=
Foreground/background multi-plane write enable
Bits 5-7
If bit 4 is a 0, data bits written into a bit map plane are stored as written. If bit 4 is a 1,
data is translated to the foreground bit (data
=
1) or into the background bit (data
=
0). This allows all selected planes to be updated simultaneously with the selected
foreground and background colors.
Reserved
Foreground/Background Register
X'lS6'
Write Only
The foreground/background register is physically contained in the data path LSI modules, with a
foreground and background bit pair implemented per plane.
Bits 0-3 Foreground color
Bit 0 Foreground plane 0 - LSI module 0
Bit 1 Foreground plane 1 - LSI module 1
Bit 2
Foreground plane 2 - LSI module 2
Bit 3 Foreground plane 3 - LSI module 3
Bits 4-7 Background Color
Bit 4 Background plane 0 - LSI module 0
Bit 5 Background plane 1 - LSI module 1
Bit 6 Background plane 2 - LSI module 2
Bit 7
Background plane 3 - LSI module 3
Advanced Color Graphics Display Adapter 9